This invention relates to the printing of color photographs onto photographic paper from color negatives, and more particularly to a method and apparatus for analyzing the color correction values necessary to achieve printing of such negatives in such a way as to produce a finished print having acceptable color rendition.
Persons familiar with color photography are familiar with the difficulty in obtaining a print which gives an acceptable color rendition of a scene originally photographed. While such difficulties are overcome to the extent necessary for color photography to have become a major industry, they remain and are most noticeable in the preparation of high quality prints from color negatives. In particular such problems arise from the variables inherently present in the color photographic process and relating to the variations in spectral response characteristics of lots of printing paper and the effects of processing variables such as chemical strength, temperatures and processing times and negative base materials. The skilled practitioner of color photographic processes will typically buy printing paper in large lots in order to stabilize the variable of lot variations, and closely control chemical strengths, temperatures and processing times. Even so, the conventional practice of the art requires that sample prints (often from "standard" negatives) be prepared daily or more often in order to confirm that acceptable color balance and rendition will be achieved in printing from color negatives.
One technical advance which has made such adjustment in processing more acceptable and lessened the need for extensive sampling in order to achieve acceptable color renditions has been the development of color printers such as that shown in U.S. Pat. No. 4,371,259 issued Feb. 1, 1983 to Howitt. As there described, it is possible to provide a colorhead means which is capable of emitting light of determinable spectral content. Such a colorhead has significantly supplanted the prior practices of preparing filter packs to be inserted optically between a light source and printing paper in order to achieve the desired printing capability, as changes in the characteristics of emitted light are much more easily accomplished. However, even with the use of such a colorhead, determination of the variables appropriate to printing from a color negative has remained a trial and error procedure.